Ferric chloride etching solutions



Patented July 27, 1954 FERRIC CHLORIDE ETCHING SOLUTIONS Theodore A. Saulnier, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware No Drawing. Application January 14, 1953, Serial No. 331,315

8 Claims.

This invention relates to ferric chloride solution compositions having improved etching properties and more particularly to such solutions especially adapted for etching copper, nickel, and alloys comprising copper and nickel.

Solutions of ferric chloride in water are employed for etching metals for many different purposes such as, for instance, to produce print ing plates and rolls such as those used for modern photoengraving and rotogravure processes, and to produce an ornamental effect upon surfaces of various metal articles. Difficulty has been encountered in the use of some available ferric chloride solutions since they give varying degrees of satisfaction as regards uniformity, smoothness and speed of etch, some solutions producing a smooth etch, others a rough etch.

In particular, etching has been found to be an especially advantageous process for the production of perforated metal screens having closely spaced, accurately located, small apertures. However, diiiiculty has been encountered in producing such screens accurately and with apertures of uniform size and spacing. Many of the ferric chloride solutions presently available produce perforated screens having apertures with rough and uneven edges and varying in size among themselves. Also, solutions previously available have been relatively slow in their action.

According to the present invention, a ferric chloride etching solution is provided containing an ammonium or alkali metal persulphate or both an ammonium or alkali metal persulphate and either nitric or hydrochloric acids or a mixture of the two. Such a solution provides etching of greatly improved quality, especially on surfaces of copper or nickel or alloys of copper and nickel. I

An object of the invention is to provide an improved etching solution.

It is another object of the invention to provide an improved ferric chloride etching solution.

It is another object of the invention to provide an improved ferric chloride etching solution particularly adaptable for etching surfaces of copper, nickel, and alloys of copper and nickel.

Still another object of the invention is to provide an improved ferric chloride etching solution capable of etching metal surfaces evenly and smoothly at a relatively high rate of speed.

These and other objects will be more readily apparent and the invention more easily understood by reference to the following detailed description.

While solutions in accordance with the invention are adaptable to a large number of different commercial processes, since etching procedures are so well known it is believed that the following single embodiment sufliciently describes the improvement brought about by theinvention.

Example A sheet or plate of copper-nickel alloy known commercially as No. 702 alloy, consisting of about 30% nickel and 70% copper and about .005 thick is coated with a light-sensitive material such as photoengravers glue of the kind known as hot-top resist. This material comprises ammonium dichromate and albumen. The sheet so coated is exposed to a light image comprising a pattern of dark-colorsd circular clots against a light background. The plate is then washed to remove the resist in the unexposed clot areas. After burning in the glue resist, the opposite side of the plate or metal sheet is coated with a strippable lacquer, paraffin wax or other suitable material. It is then etched at room temperature by any suitable method such as spraying or agitating in a tray using a ferric chloride solution having a specific gravity of 38 to 42 Baume to which has been added about 50 grams per liter of ammonium persulphate and 2% by volume concentrated nitric acid.

The etching solution corrodes and removes the metal in the dot areas from which the resist coating has been washed away. In about fifteen minutes, the solution has etched completely through the metal sheet and has formed holes that very closely correspond in size and shape to the dot areas originally exposed upon the metal surface by washing off the resist. The holes so formed are much more uniform, have smoother and rounder edges and are more rapidly formed than by ferric chloride etching solutions previously known. After the remaining resist material has been removed by any suitable means, such as a suitable solvent or by rubbing, the screen is complete.

The resist material described is subject to some degree of chemical attack by ferric chloride solutions according to the invention; therefore, it is generally desirable when using this particular resist in the practice of the invention to remove the resist material subsequent to the etching process. With other resist materials it may be desirable to leave the resist upon the surface of the screen, although this will be determined to a large extent by the use desired to be made of the etched product.

Solutions according to the invention give excellent results when used at room temperatures, 1. e., from about 50 F. to 90 ER, and the use of elevated temperatures is not generally recommended since the etching action becomes more rapid and is more difficult to control; however, in certain applications it may be desirable to operate the solutions at temperatures of up to about 130 F.

While there has been described a preferred embodiment of the invention, greatly improved etching has also been found to result from the use of a ferric chloride solution having a specific gravity of 35 to 48 Baum and containing ammonium or alkali metal persulphates or a mixture of ammonium and alkali metal persulphates in an amount of about 20 to 50 g./l. In the etching of copper, nickel, and alloys of copper and nickel, particularly advantageous results are achieved when to this solution is added about 2% to 10% by volume concentrated nitric acid, concentrated hydrochloric acid or a mixture of nitric and hydrochloric acids.

Since materials commonly subjected to etching processes are so many and varied, and since the objects desired in diiferent etching processes vary so widely, it is difficult to attempt to list all of the different properties of the different solutions within the range of compositions described. Sometimes it is desirable to etch a difficultly etched metal rapidly, and on the other hand, it is sometimes desirable to etch an easily etched metal slowly depending upon the result desired. Solutions according to the invention provide a wide range of etching speeds, and in general, they etch with a higher degree of uniformity than solutions previously available.

While only a single example has been given it should be understood that compositions in accordance with the invention are generally useful for all types of etching upon copper and nickel surfaces, and that the invention is not limited to the production of perforated screens or to an etching process wherein the solution corrodes completely through a metal sheet to per forate it. Solutions in accordance with the invention are suitable for all types of etching, and are particularly useful where smoothness and uniformity of etching action is desired.

There have thus been described novel and improved ferric chloride etching solutions which etch evenly and smoothly and are particularly adaptable to etching surfaces of copper, nickel, and alloys of copper and nickel.

What is claimed is:

1. An etc ,1, composition comprising a waion of ferric chloride having a specific or 35 to 48 Baunr, 20 to 50 grams per liter of a substance selected from the group con sisting of ammonium persulfate, alkali metal persulfates, and a mixture of ammonium and alkali metal persulfates, and 2% to 10% by volume of a substance selected from the group consisting of concentrated hydrochloric acid, concentrated nitric acid, and a mixture of hydrochloric and nitric acids.

2. An etching composition comprising an 4 aqueous solution of ferric chloride having a specific gravity of 38 to 42 Baume', about 50 grams per liter ammonium persulfate, and about 2% by volume concentrated nitric acid.

3. In the method of etching a copper surface, the step comprising placing said surface into contact with a composition of matter comprising a water solution of ferric chloride having a specific gravity of 35 to 48 Baume, 20 to 50 grams per liter of a substance selected from the group consisting of ammonium pesulfate, alkali metal persulfates, and a mixture of ammonium and alkali metal persulfates, and 2% to 10% by volume of a substance selected from the group consisting of concentrated hydrochloric acid, concentrated nitric acid, and a mixture of hydrochloric and nitric acids.

4. In the method of etching of nickel surface, the step comprising placing said surface into contact with a composition of matter comprising a water solution of ferric chloride having a specific gravity of 35 to 48 Baum, 20 to 50 grams per liter of a substance selected from the group consisting of ammonium persulfate, alkali metal persulfates, and a mixture of ammonium and alkali metal persulfates, and 2% to 10% by volume of a substance selected from the group consisting of concentrated hydrochloric acid concentrated nitric acid, and a mixture of hydrochloric and nitric acids.

5. In the method of etching a surface consisting essentially of an alloy of copper and nickel, the step comprising placing said surface into contact with a composition of matter comprising a water solution of ferric chloride having a specific gravity of 35 to 48 Baurn, 20 to 50 grams per liter of a substance selected from the group consisting of ammonium persulfate, alkali metal persulfates, and a mixture of ammonium and alkali metal persulfates, and 2% to 10% by volume of a substance selected from the group consisting of concentrated hydrochloric acid, concentrated nitric acid, and a mixture of hydrochloric and nitric acids.

6. In the method of etching a surface sisting essentially of an alloy of copper and nickel, the step comprising placing said surface into contact with a composition of matter comprising an aqueous solution of ferric chloride having a specific gravity of 38 to 42 Baum, about 50 grams per liter ammonium persulphate, and about 2% by volume concentrated nitric acid.

7. The method in accordance with claim 5 COD- -' in which said step is carried out at a tempera- References Gited in the file of this patent UNITED STATES PATENTS Number Name Date 1,903,778 Conroy Apr. 18, 1933 2,000,576 Boller May 7, 1935 2,409,271 Goldowski Oct. 15, 1946 

1. AN ETCHING COMPOSITION COMPRISING A WATER SOLUTION OF FERRIC CHLORIDE HAVING A SPECIFIC GRAVITY OF 35* TO 48* BAUME, 20 TO 50 GRAMS PER LITER OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF AMMONIUM PERSULFATE, ALKALI METAL PERSULFATES, AND A MIXTURE OF AMMONIUM AND ALKALI METAL PERSULFATES, AND 2% TO 10% BY VOLUME OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF CONCENTRATED HYDROCHLORIC ACID, CONCENTRATED NITRIC ACID, AND A MIXTURE OF HYDROCHLORIC AND NITRIC ACIDS. 